1. Field of the Invention
The present invention relates to a new and improved pressure relief valves with adjustable set pressure and to a new and improved method for adjusting the set pressure.
2. Description of the Background Art
To relieve product pressures at a predetermined value of relief thereby protecting the product container or vessel, pressure relief valves employing vertically guided horizontal valve pallets have been used. The valve pallet cooperates with a valve seat within a chamber in the valve housing. Since many of the products contained in the vessels are corrosive or contaminating in nature, it is a regular and necessary practice to examine the sealing surfaces of the valve pallet and associated valve seat. The construction of the typical valve, however, makes inspection of the valve pallet and seat a difficult and often hazardous task due to relatively large spring forces employed to apply a set pressure biasing the valve pallet into engagement with the valve seat. In order to inspect the typical pressure relief valve of this type, the product pressure must be removed from the vessel and the internal forces of the biasing member relieved by mechanical means that often require working within the valve housing. Once the inspection is completed and the valve reassembled, the set pressure of the spring must be recalibrated. During these inspections, serious injury to the inspector is always possible. Avoidance of these dangers during inspection and operation of the valve is desirable.